gdb on Mac OS bpt implementation question

[Mick Jordan <mick dot jordan at oracle dot com>]

I'd be grateful if someone could point me to where in the gdb source 
code that Mac OS specific breakpoint setting is done. The problem I am 
trying to resolve is how breakpoints are set in shared libraries, given 
that they are loaded read-only on Mac OS X (assuming the "write a bpt 
instruction" approach). The context for this is a custom debugger we 
have for a Java VM (Maxine) which uses "write a bpt instruction" and 
works fine setting breakpoints in shared library code on Linux and 
Solaris, but not on MacOS (we get access faults trying to write the BPT 
instruction).

Thanks
Mick Jordan